I have yet to master the large form. More specifically, I've yet to manage a large form successfully without bending to the age-old dogma of "goal-oriented music"—that is, I haven't been able to write a long piece while staying true to my current aesthetic concern of writing strong music that is not interested in "going anywhere." It's something which requires a lot of experimentation with musical time and the handling of material in such a way that no true development is perceived in the traditional sense; very difficult.
I also have significant difficulty writing for winds and brass.

here is a blog post.
it is about mozart.
specifically, it is about mozart's 8th sonata for the fortepiano.
if you would like to to read it, please do.
or not.
that would be ok, too.
http://music-and-prittee-girls.blogspot.com/2012/06/mozart.html